LCD TV power Supply TOM202CABB Trouble Shooting. All caps replaced.

Discussion in 'General Electronics Chat' started by RealtyRod, Aug 27, 2014.

  1. RealtyRod

    Thread Starter New Member

    Aug 27, 2014
    5
    1
    SUMMARY
    ======
    I am presently attempting to repair a Digital Research WT322 aka DLCD32 with a Starmen Tom202cabb power supply. This power supply appears to be used in these TVs as well.
    Emprex WT323
    DIGITAL LIFESTYLES LT26407
    DIGITAL LIFESTYLES Research WT322
    SOYO MT-SYTPT2627AB
    SOYO MT-SYTPT3227AB
    SOYO MT-SYTPT3227AB

    The main symptom is the Power LED is completely dead. Nothing happens when the power button is pressed. It is not even red in standby. It does not turn green when power button is pressed. The 5a slow blow fuse is popped. I replaced all of the caps on the power supply as there were 2 that were bulged.

    As I am new to working on power supplies, I would appreciate any help steering me in the right direction to troubleshoot this power supply. Is there a way to obtain the SCHEMATIC for this item?


    OBSERVATIONS
    = = = = = = = = = =
    1. No life whatsoever. No LED or sounds at all.
    2. Fuse is blown.
    3. Caps bulged -1500uf 16v C37 and 150uf 400V C09.
    4. 120v measured at incoming to fuse. Other side has no reading. Removed fuse. Reads open.
    5. Juncture of Q3 a [2SK3502 (N-Channel Power MosFet)],R21, RB1, D3 and D23 appears darker on the board.

    TASK ACCOMPLISHED so far
    = = = = = = = = = = = = = = = = =
    1) Replaced all 14 capacitors.
    2) After replacing capacitors and fuse, tested continuity on power supply 5 amp slow blow fuse again. It is blown. Reads Infinity.
    3) Identified most of components on the board for testing or replacement.

    Photos Included – If better photos needed I can dust off my Canon PowerShot Pro.
    = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
    1- Model Number Identification
    2- PS Board Top View
    3- PS Board Bottom View
    4- PS Board Left View
    5- PS Board Right View
    6- Q3 suspicious area
    7- Bulged Caps that led to replacing all capacitors.
    8- Comparison of Large Cap replacement

    Parts Identified on Board so far
    ===========================
    BD2 – GBU606 (Bridge Rectifier)
    Q1 – FQPF13N50C (N-Channel Qfet MosFet)
    Q3 – 2SK3502 (N-Channel Power MosFet)
    Q5 – 2SK3115 (Switching N-Channel Power MosFet)
    Q11 – Unable to See because of Obstruction

    D5 – MBR20150CT (Dual High Voltage Schottky Rectifier)
    D6 - MBR20150CT (Dual High Voltage Schottky Rectifier)
    D10 – MS865C10 (Low IR Schottky Barrier Diode)
    D11 – SB2020FCT (Isolation Schottky Barrier Rectifier)
    D20 - ????No Name on Part
    PH1, PH2 & Ph3 - L0730 817B Photo Transistor Opto-Coupler
    IC6 – TL431k Adjustable 3 Terminal Voltage Regulator

    PROBLEM
    ======
    1) The power LED is not RED in standby mode. Press the power button and the power LED does not turn GREEN.
    2) Tested continuity on power supply 5 amp slow blow fuse. It is blown. Reads Infinity.

    QUESTION
    = = = = = = =
    1. How to obtain Schematic for the TOM202CABB? I have sent email to Starmen.com.tw to see if they can help.
    2. How to Trouble Shoot power supply in general?
    3. How to Trouble Shoot Tom202cabb in particular?
    4. How to test un-powered board components in place if possible?
    5. How to test discrete components if taken off board?


    LESSONS LEARNED SO FAR
    = = = = = = = = = = = = = = = = =
    1. Soldering caps is MUCH easier if you tin the leads and use FLUX. Flux in solder is not enough. Only takes a second or 2 for solder to connect joint.
    2. Caps are not the only item to go bad in a power supply. Quite a few people sell KITS for this Power Supply.

    Thoughts on moving forward – Preliminary Plans
    = = = = = = = = = = = = = = = = = = = = = = = = =
    1. Test all components on the board if possible. Concentrating on Q3 and that area as a start.
    Will POST results of component tests. Starting with Q3.
    2. Test all components required to be removed and isolated from board.
    3. Hopefully diagnosis will ID bad component.
    4. If no ID. Replace all components if possible.
    5. Obtain used replacement TOM202CABB as last resort.

    Any help and insight would be Greatly Appreciated.

    RealtyRod
     
  2. BR-549

    Well-Known Member

    Sep 22, 2013
    1,981
    388
    I would suggest a scope and an octopus component tester. You can troubleshoot an unpowered, undocumented board in a few moments.
     
  3. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    Do you have any pictures of the board itself. Quite often on TV sets you will find that they are labelled for their outputs to the TCON board, mainboard and inverter boards. There is usually 24V, 12V 5V and 3V but they may not all appear depending on TV set. I would start with these voltage checks if they are labelled. Be sure to use an isolation transformer and if you don't know what you are doing, it can be very dangerous in there and you should have a professional look at it. Pictures please if you dare to continue.
     
  4. RealtyRod

    Thread Starter New Member

    Aug 27, 2014
    5
    1
    Br-549 - Thanks for the info about the OCTOPUS. I will work on creating one. Will dust off my Oscope.

    bwilliams60 - Thanks for the response. I am including the photos which I failed to load initially.

    1- Model Number Identification
    2- PS Board Top View
    3- PS Board Bottom View
    4- PS Board Left View
    5- PS Board Right View
    6- Q3 suspicious area

    RealtyRod
     
  5. RealtyRod

    Thread Starter New Member

    Aug 27, 2014
    5
    1
    I am including photos of the 2 bad caps which lead me to replacing all of the caps.
    Also, does anyone know how I can obtain the schematic for the TOM202CABB power supply?

    Thanks again,
    RealtyRod
     
  6. Gdrumm

    Distinguished Member

    Aug 29, 2008
    684
    36
    On the 6th picture, the K3502 appears to be burnt and bulging.

    Marked Q3 on the board.
     
    Last edited: Aug 28, 2014
  7. RealtyRod

    Thread Starter New Member

    Aug 27, 2014
    5
    1
    Thanks Gdrumm.
    Is there a way to test this MOSFET without taking it off the board?

    Q3 – 2SK3502 (N-Channel Power MosFet)

    I am thinking of removing it for testing.

    Also where can I find a replacement? I checked Digikey and Mouser they both do not have this part. I could only find it on EBAY or Amazon from China.

    RealtyRod
     
  8. Gdrumm

    Distinguished Member

    Aug 29, 2008
    684
    36
    It is my understanding that it must be removed to be tested.

    I'm pretty sure it's fried, by the look of it.

    Components nearby may also be compromised.

    I don't know of an easy way.

    I'm doing something similar on an LCD TV, and it's a pain.

    Gary
     
    Last edited: Aug 28, 2014
  9. dave0885

    New Member

    Aug 28, 2014
    1
    0
    in my experience with power suplys ive always found the diodes to be suspect, so I always replce them, if one has shorted this would pop the fuse and stop your led from lighting
     
  10. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    I was noticing the same thing as well as the discoloration around the diode area. Check the mosfet off the board and check all components in thar area. You will most likely be getting this mosfet from japan if needed. Use findchips.com when locating ic's.
    I was just looking at this a little closer. If you look at my picture that I clipped from yours, I believe I am looking at the main capacitor connections. Are these good solder joints? Hard to tell from the picture but they look odd. Also the discoloration around the area in black leads me to believe that Gdrumm made a great observation with the MOSFET. I am thinking we are in the right area.
     
    Last edited: Aug 28, 2014
  11. RealtyRod

    Thread Starter New Member

    Aug 27, 2014
    5
    1
    Thanks for the replies.
    In process of removing Q3.
    Will re-solder large cap with FLUX.

    Preliminary checks of diodes of D3 & D23 are .547 one way and Open the other way for both.
    Checking RB1 is Shorted (0.000) reading in Both directions. Not quite sure what RB1 is yet.

    RealtyRod
     
  12. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    I see there is an RB2 near the large capacitor. Can we get any information from it. Not saying they are the same but we can identify what RB is unless someone else has the answer.
     
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